Radio direction finder



Dec. 30, 1941.

MPL /F/EH w. VAN B. ROBERIS 2,268,085l

RADIO DIRECTION FINDER Fild oct. 1'2, 1959 u yq D n m ""lh S m Tl"- l'l"www @www m D @D 311Dentor I ww . (Ittorne 1 Patented Dec. 30, 1941 RADIODIRECTION FINDER Walter van B. Roberts, Princeton, N. J., assignor toRadio Corporation of America, a corporation of Delaware ApplicationOctober 12, 1939, Serial No. 299,200

8 Claims. (Cl. 25u-1l) This invention relates to radio direction ndtion.The 'term clock position as here used ers generally and particularly toan arrangement may be explained as follows: If the antenna axis forindicating the direction of the location of a is pointed slightly totheright of the source of radio transmitter in two intersecting planes.signals, the clock position is said to be 3 oclock,

One of the objects of the invention is to prowhile, if it is *pointed`below the source, it is at 6 vide means for indicating simultaneouslyboth oclock, and so on'.

the horizontal and vertical deviations between The voltage developed incircuit I is impressed the axis of a directive antenna and the direcon adifferential translating and modulating detion from the antenna to asource of plane polarvice T whereby in the balanced condition of theized radio waves. Another object is to provide i0 device no currentflows in coil LI connected in means for indicating the electric andmagnetic its output. However, the device T is periodically fieldcomponents of a radio wave to indicate the unbalancedby the applicationof a differential wave source. An additional object is to provide ormodulating Voltage which is derived from a means for indicating thedeviation and sense of relatively low frequency alternating voltagedeviation between the axis of an antenna system source M. Thus, thecurrent through LI is and a line from the antenna through the` wavevaried sinusoidally in magnitude between altersource. nately positiveand negative limits; that is, its

The operation of the invention will be best polarity is' periodicallyreversed as its magnitude understood by reference to the accompanyingpasses through Zero. The voltage developed by dlaWiIlg in Whichv Figure1 iSV ai SChematiC da- 20 this current is amplified by means of anamplifier gram representing the circuit arrangement of 2 and impressedby way of transformer primaries the invention' and Figure 2 is a vectordiagram L2 and L3 upon resonant circuits 3 and 4. At the of certainvoltage relations existing in the aforesame time, these two resonantcircuits are supsaid circuit. plied'with relatively large andsubstantially equal Referring to Fig. 1, the reference character'I-IV Jquadrature voltages derived from a nondirecindicates a directionalantenna comprising an tional antenna 5, amplifier B, phase shifter 'land open or dipole portion adapted to derive voltages phase splitter 8.The equal quadrature voltages from radio waves whose electric vector hasa are applied by way of coils-Lll'and L5 to the rescomponent parallel tosaid open portion anda onant circuits 3, 4 respectively. It will at thisclosed or loop antennaportion adapted to derive 3 point be advisable tovindicate the nature of the voltages from radio waves whose magneticvectotal voltages developed in the resonant circuits tor has a componentparallel to the loop' axis. 3 and'll. Preferably, the relativedimensions of these two Referringv to Fig. 2, the vector eA representsportions are so chosen that the total voltage thenondirectional voltagecomponent in circuit picked up by the composite antenna, when the It 3,while the vector eB represents the nondirecaxis ofthe structure makes agiven angle with tional `voltage in circuit The vector e reprethedirection of propagationv of the-waves, is the sents the relativelysmall signal frequency voltsame for all possibleclock positions ofthe'anage impressed on both of the circuits 3 and 4 at tenna axis. Whilethis condition will be met exa given instant. Since this voltage e iscontinuactly only at a single frequency, over a small 40 ally varying inmagnitude, as explained above,

range offrequencies it may be attained suflicientthe resultant voltagein `each of the circuits 3 ly closely. for practical purposes. Thislimitation and 4 may be represented by a vector extending is. dueto thefact` that. the relative voltage pickups from the point il to one of thedash lines whose of the two antenna portions varies with fredirection isthe same as that of e. As e varies quency. It, is furthermore preferableto so. diin magnitude, the resultant vector moves back mension the twoportions that the system is resand forth along the appropriate dashline. Thus, onant at or near the desired frequency of operit is seenthat if e is small compared to eA and ation. A link circuit L isemployed to transferes, the amplitude variation of the resultantvoltenergy picked up by the antenna system to the age in circuit 3 willbe determined by the comresonant circuit I. Thus there isv producedv inponent of e that is in phase with eA while the circuit l' a signalvoltage whose magnitude is deamplitude variation of the resultantvoltage in termined by the angle between the antenna axis circuit dwill' be determined by the component and the direction of propagation ofthe incomof' that is in phase with eB.

ing signal waves but whose phase is determined The' resultant voltage incircuit 3 is impressed bythe clock position or sense of thefdeviaon aAdiode rectifier D2 and the alternating current output of this diode isimpressed on a vertical deiiection element of cathode ray tube CR. Thusthe low frequency voltage component on these plates is in phase with thevoltage of source M; the magnitude is determined by the component of ethat is in phase with eA. Similarly, a low frequency voltage componentis impressed on the horizontal deflection elements of the cathode raytube CR. This low frequency voltage component is also in phase with thevoltage from the source M; the magnitude is determined by the componentof e that is in phase with eB. Since the two deflection voltages on thedeiiecting elements have like phase, the cathode ray spot will trace astraight line whose inclination is determined by the relative magnitudesof the deiiection voltages. Hence the clock position of this line has anangular value that depends linearly on the angular position of thevector e. But as explained before, the angular position of e, that is tosay the phase of e, is determined by the clock position of .thedeviation between the antenna axis and the direction of signalpropagation. Hence, iinally, the clock position of the cathode ray tracevaries linearly with the clock position of this deviation while thelength of the trace is determined by the magnitude of the deviation.

For convenience in reading, it is desirable that the clock position ofthetrace should coincide with that of the antenna. This may be mosteasily arrangedl by adjusting the phase of the nondirectional voltage bymeans of the phase shifter 1 following amplifier 6 in the nondirectionalchannel. This may be done by pointing the antenna HV `directly at thesource as indicated by the length of the cathode ray trace shrinking toa single spot. Then the antenna is swung in a known direction, say tothe right, so as to cause an extended linear trace. Then the phaseadjuster is operated to make the trace horizontal. However, a merehorizontal trace does not indicate whether the deviation is right orleft.

In order to indicate sensej a voltage derived from the same lowfrequency source M is applied, together with a constant biasing voltage,to the cathode ray tube grid so as to cause unequal brightness on thetwo halves of the trace. A constant negative bias may be used that issumciently large so that only near the positive peak` of the Variablevoltage on the grid does the cathode ray spot show at all. In this, casethe phase shifter 9, shown between the source M and the grid, may beomitted as the grid voltage will be at a maximum simultaneously with theposition of the spot and all that is necessary is to choose the polarityof the voltage applied to the grid such as to give the desired senseindication.

While, for the purpose of simplifying the explanation, it was assumedthat amplification of the signal voltage was performed at signalfrequency, it will be understood that the same results will be obtainedif both the directional and nondirectional voltages are changed infrequency by a common heterodyne oscillator, as is well known to thoseskilled in the art. The frequency change may be performed either beforeor after the differentiating and modulating step performed by the deviceT.

It will be understood that, While a particular form of antenna has beendescribed, the invention may equally well make use of any other sort ofantenna system which will pick up and transfer to a utilization circuita voltage whose phase is substantially determined by the clock positionor sense of deviation, while its magnitude is substantially independentof clock position but determined by the magnitude of the deviation. Theinvention is useful in the instrument landing of aircraft, in thedetermination of the location of radio transmitters, especially onaircraft in flight, in indications of radio Wave propagation, and inlikeuses,

What is claimed is:

1. A radio direction finder including in combination an antenna systemresponsive to radio waves to obtain voltages therefrom, said voltageshaving a magnitude determined by the magnitude of the deviation betweenthe line of wave propagation and the axial line of said antenna systemand having a phase determined by the sense of said deviation, means formodulating said voltages, means for deriving from said waves a voltageindependent of said deviations, means for obtaining voltages ofquadrature phase from said last-mentioned voltage, a pair of detectors,means for applying said modulated voltages and one of said quadraturephase voltages to each of said detectors respectively, and meansconnected to the outputs of said detectors for indicating the ydirectionof the source of said radio waves in terms of horizontal and verticalcoordinates as a function of the output voltages of said detectors.

2. A radio direction finder including in combination an antenna systemincluding a loop and a dipole arranged so that the loop connects theelements of the dipole and has its axis in substantial alignment Withthe axis of the dipole, said antenna system deriving voltages from theWaves whose source is to be indicated, said voltages having a magnitudedetermined by the magnitude of the deviation between the line of Wavepropagation and the axial line of said antenna and having a phasedetermined by the sense of said deviation, means for modulating saidvoltages, means for deriving from said waves a voltage independent ofsaid deviations, means for obtaining voltages of quadrature phase-fromsaid last-mentioned voltage, a pair of detectors, means for applyingsaid modulated voltages and one of said quadrature phase voltages toeach of said detectors respectively, and means connected to the outputsof said detectors for indicating the direction of the source of saidradio Waves in terms of horizontal and vertical coordinates as afunction of the output voltages of said detectors.

3. A radio direction iinder including in combination an antenna systemresponsive to radio waves to obtain voltages therefrom, said voltageshaving a magnitude determined by the magnitude of the deviation betweenthe line of wave propagation and the axial line of said antenna systemand having a phase determined by the sense of said deviation, means formodulating said voltages, means for deriving from said waves a voltageindependent of said deviations, means for obtaining voltages ofquadrature phase from said last-mentioned voltage, a pair of detectors,means for applying said modulated voltages and one of said quadraturephase voltages to each of said detectors respectively, and a cathode raytube having pairs of deiiecting elements, said pairs being connectedrespectively to the outputs of said detectors for indicating the sourceof said radio waves in terms of horizontal and vertical coordinates as afunction of the output voltages of said detectors and the resultingcath- 6. A radio wave source indicator including an antenna system forderiving from said Wave voltages having a magnitude determined by thedeviation between the line of propagation of said wave and the axialline of said antenna system and having a phase determined by the senseof said deviation, means for applying said voltages to a balancedmodulator, a source of modulation voltages, means for applying saidmodulation voltages to said modulator, a nodirectional antenna forderiving voltages from said Wave, means for obtaining from saidlast-mentioned voltages radio frequency voltages of quadrature phase, apair of detectors, means for applying voltages from said balancedmodulator to said detectors, means for applying to said detectorsrespectively said radio frequency voltages of quadrature phase, acathode ray tube having pairs of dei'lecting elements, and meansconnecting one of said pairs of deflecting elements to one of saiddetectors and the other of said pairs of deectlng elements to the otherof said detectors whereby said cathode ray is deiected as a function ofthe output voltages of said detectors to indicate the wave source interms of horizontal and vertical coordinates.

'1. In an indicator of the character of claim 6, means for varying theintensity of said cathode ray and means for applying said modulationvoltages to said cathode ray intensity varying means to indicate thesense of the direction of said wave source.

8. In a direction indicating system, the combination of an antennasystem adapted to pick up a signal voltage Whose magnitude is determinedby the magnitude of the deviation between the direction of signalpropagation and a line determined by said antenna system but whose phaseis determined by the orientation of said deviation, means for amplifyingsaid voltage, means for periodically varying the amplitude of saidvoltage, a pair of detectors, means for applying said amplified voltageto said detectors, a nondirectional antenna and means for derivingtherefrom two phases of signal frequency voltages, connections forapplying one of said phases to one of said detectors and connections forapplying the other of said phases to the other of said detectors and asingle means connected to the outputs of said detectors for indicatingthe relative magnitudes of the output voltages of said detectors.

WALTER VAN B. ROBERTS.

